It is well known to use ethylene oxide as a sterilizing gas. Ethylene oxide in pure form, however, is highly poisonous and can be explosive. Consequently, ethylene oxide is commercially delivered as a mixture having a low level of ethylene oxide distributed in an inert gas. U.S. Pat. No. 2,891,838 to Kaye, U.S. Pat. No. 3,238,096 to Kaye and U.S. Pat. No. 4,954,284 to Batt et al. describe such systems. The inert gas choice has been Freon 12, which is dichlorodifhoromethane. As is well known, the use of chlorofluoro compounds is being phased out of commercial use. It would be highly desirable to provide a commercial mixture of ethylene oxide in an inert gas which is not hazardous or harmful to the atmosphere. A highly desirable inert gas for use with ethylene oxide is carbon dioxide. However, in the liquid state ethylene oxide is only partially miscible with carbon dioxide. When placed in a pressurized cylinder, the carbon dioxide tends to occupy the head space of the cylinder as the mixture of gases is dispensed. Consequently, the ethylene oxide in the liquid phase becomes increasingly more concentrated as the gas undergoes dispensing. This complicates the use of the ethylene oxide as a sterilizing medium since the amount of gas to be used is uncertain because of the concentration gradient that occurs during the dispensing process. The problems of using carbon dioxide as a diluting gas are described in U.S. Pat. No. 5,128,101 to Boynton.
U.S. Pat. No. 2,007,738 to Baer early recognized the desirability of using ethylene oxide and carbon dioxide. The Baer patent recognized the problem of immiscibility of ethylene oxide and carbon dioxide. The solution to this problem was solved in the Baer patent by dispensing the entire contents of a liquid mixture of ethylene oxide and carbon dioxide to an accumulator which was at a lower pressure. The two gases vaporize and the gaseous mixture in the accumulator could be dispensed with a constant level of ethylene oxide in the mixture of gases.
U.S. Pat. No. 2,965,936 to Kaye also discloses a one-shot ethylene oxide and carbon dioxide mixture which was dispensed from an ampoule which provided small amounts of an ethylene oxide and carbon dioxide mixture.
It would be highly desirable to provide a means for dispensing desired amounts from a large source of ethylene oxide and carbon dioxide wherein the concentration of the ethylene oxide could be maintained relatively constant throughout the dispensing process.
Accordingly, it is a principal object of the present invention to provide a system for dispensing a liquid mixture of ethylene oxide and carbon dioxide, wherein the ethylene oxide level remains relatively constant throughout the dispensing process.